There are soooo many communication features of hotspot devices and smart phones that improve with each new iteration of both. As a previous poster mentioned, if you do purchase a new hotspot/jetpack (same thing) don't let anyone sell you outdated technology. Often the clerks in the stores don't know the difference.
If you go with an AT&T plan, get their Nighthawk hotspot. If you choose a Verizon plan, you'll want the 8800L.
I'm not sure what a previous poster meant by "the iPhones on LTE are twice as fast as ATT" as all modern AT&T phones and hotspots use LTE.
Speeds will vary by available cell towers(Verizon, AT&T,etc.) in each location. The fastest solution in location "A" may be sub-par in location "B".